In UTRA TDD mode the synchronization channel (SCH) has two functions. The primary function is to provide a signal that enables a ‘UE’ (user equipment, such as a wireless terminal) to search for and identify a ‘Node B’ (i.e, a wireless Base Station of a UMTS system). The secondary function is to provide sufficient information to allow a UE to demodulate a P-CCPCH (Primary Common Control Physical CHannel) transmission and obtain the system information, sent on the BCH (Broadcast Channel) transport channel which is carried by the P-CCPCH, needed in order to be able to communicate with the network. The physical channel P-CCPCH has the characteristics of the Beacon Function, as defined in the technical specification ‘3GPP TS 25.221’ publicly available on the of the 3.sup.rd Generation Partnership Project.
There are two cases of SCH and P-CCPCH allocation as follows: 1. Case 1) SCH and P-CCPCH allocated in timeslot #k, where k=0 . . . 14 Case 2) SCH allocated in two timeslots: timeslot #k and timeslot #k+8, where k=0 . . . 6; P-CCPCH allocated in timeslot #k where timeslot #k is the k.sup.th timeslot. Due to this SCH scheme, the position of P-CCPCH is known from the SCH. The SCH consists of one real-valued primary synchronization code (PSC) and three complex secondary synchronization codes (SSCs), all of length 256 chips. The PSC is common for all Node Bs, but the SSCs are Node B specific. The PSC and SSC are transmitted simultaneously from a given Node B at a specific fixed time offset (t.sub.offset) from the start of the timeslot. The time offset is included to prevent the possible capture effect that would otherwise occur as a consequence of all Node Bs transmitting the common primary code at the same time.
Automatic Frequency Correction (AFC) is typically employed in UTRA TDD mode to correct for frequency offsets occurring in the presence of noise in the received signal. In UTRA TDD mode the PSC typically operates in negative values of SNR, which with conventional methods of AFC give rise to a large frequency offset, degrading performance.
A need therefore exists for frequency correction wherein the abovementioned disadvantage(s) may be alleviated.